Feature and depth measurement using multiple beam sources and interferometry

ABSTRACT

Systems and techniques for processing materials using wavelength beam combining for high-power operation in concert with interferometry to detect the depth or height of features as they are created.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of U.S. ProvisionalPatent Application No. 61/973,353, filed on Apr. 1, 2014, the entiredisclosure of which is hereby incorporated herein by reference.

FIELD OF THE INVENTION

In various embodiments, the present invention relates generally tobeam-emission systems, and more particularly to systems and techniquesfor processing materials.

BACKGROUND

High-power lasers are used in many cutting, etching, annealing, welding,drilling, and soldering applications. An advantage to these systems isthe precision with which cuts can be made and recesses etched into awide variety of materials.

One challenge in implementing high-precision laser-based processingsystems is determining the height or depth of a feature as it is formed.Material anisotropy, or even ordinary compositional variations across anominally uniform material, can affect the amount of material removed bya laser at a given power level. Without real-time knowledge of featuredepth or height during processing, and feedback capability to alter thebeam in response thereto, it is impossible to guarantee precisedimensions that do not vary across the feature particularly if thefeature extends across a considerable (e.g., more than a few microns)length, since the more material that is processed, the greater will bethe likelihood of encountering compositional variations that affectmaterial response.

SUMMARY

Embodiments of the invention provide systems and techniques forprocessing materials using wavelength beam combining for high-poweroperation in concert with interferometry to detect the depth or heightof features as they are created.

Interferometry makes use of the principle of superposition to combinewaves such that their combination is diagnostic of the original state ofthe waves. This works because when two waves with the same frequencycombine, the resulting pattern is determined by the phase differencebetween the two waves—i.e., waves that are in phase will undergoconstructive interference while waves that are out of phase will undergodestructive interference. Thus, depending on the height or depth of afeature in relation to the wavelengths of the incident radiation, somewavelengths, when combined with their reflections, will undergo thesechanges, which indicate the true depth/height of a feature—e.g., a cut,weld, or mesa. By utilizing a two-dimensional (2D) beam, the structureof a 3D feature can be determined. Feature information can be used in afeedback configuration to ensure that the entire feature remains uniformas it is created.

Accordingly, in a first aspect, the invention pertains to a system forprocessing a workpiece. In various embodiments, the system comprises awavelength beam combining (WBC) emitter for emitting a multi-wavelengthoutput beam comprising optical radiation having a plurality ofwavelengths; a movable surface reflective to all of the wavelengths inthe multi-wavelength output beam; a photodetector; a beamsplitter for(i) diverting a portion of the multi-wavelength output beam to themovable reflective surface and (ii) diverting a portion of a reflectionof the multi-wavelength output beam from a surface of the workpiece tothe photodetector, the photodetector being aligned with the movablereflective surface to receive therefrom a reflection of the divertedportion of the multi-wavelength output beam; and a controller, coupledto the WBC emitter device and the photodetector, for computing a heightor depth of a feature on the surface of the workpiece based at least inpart on a signal from photodetector.

The height or depth may be determined based on a distance between thebeamsplitter and the surface of the workpiece. This, in turn, may bedetermined from the signal from the photodetector, which may indicatethe degree of interference between the reflection of themulti-wavelength output beam from the surface of the workpiece and thereflection from the mirror of the diverted portion of themulti-wavelength output beam.

In various embodiments, wherein the controller is configured to controla parameter of the multi-wavelength output beam to maintain a targetdistance between the beamsplitter and the surface of the workpiece. Forexample, the controlled parameter may be one or more of power or beamparameter product. The WBC emitter may comprise a plurality of beamemitters each emitting a beam; a combining optical element arranged toreceive the plurality of beams and cause a chief ray of each of thebeams to converge along a beam-combining axis; a dispersive element,positioned along the beam-combining axis, to receive and transmit theconverging chief rays; and a partially reflective output couplerarranged to receive the transmitted beams from the dispersive element,to reflect a portion of the transmitted beams toward the dispersiveelement, and to transmit the multi-wavelength output beam.

In another aspect, the invention pertains to a method for processing aworkpiece. In various embodiments, the method comprises the steps ofcausing emission of an output beam from a WBC emitter, where the outputbeam comprises optical radiation having a plurality of wavelengths;diverting a portion of the output beam to a movable surface reflectiveto all of the wavelengths in the multi-wavelength output beam; divertinga portion of a reflection of the output beam from a surface of theworkpiece to a photodetector; receiving, at the photodetector, areflection from the movable reflective surface of the diverted portionof the output beam, the reflection including all of the wavelengths inthe multi-wavelength output beam; and computing a height or depth of afeature on the workpiece based at least in part on a signal from thephotodetector.

The height or depth may be determined based on a distance between thesurface of the workpiece and a location where the portion of thereflection is diverted. For example, the signal from the photodetectormay indicate a degree of interference between the reflection of themulti-wavelength output beam from the surface of the workpiece and thereflection, from the movable surface, of the diverted portion of themulti-wavelength output beam.

In some embodiments, the method further comprises the step ofcontrolling a parameter of the multi-wavelength output beam to maintaina target distance between the beamsplitter and the surface of theworkpiece. For example, the controlled parameter of the multi-wavelengthoutput beam may be power and/or beam parameter product.

As used herein, the term “optical element” may refer to any of lenses,mirrors, prisms and the like which redirect, reflect, bend, or in anyother manner optically manipulate electromagnetic radiation. The term“beam” includes any form of directed electromagnetic radiation, and maybe single-wavelength or multi-wavelength. Beam emitters, emitters, orlaser emitters, or lasers include any electromagnetic beam-generatingdevice such as semiconductor elements, which generate an electromagneticbeam, but may or may not be self-resonating. These also include fiberlasers, disk lasers, non-solid state lasers, vertical cavity surfaceemitting lasers (VCSELs), etc. Generally, each emitter includes a backreflective surface, at least one optical gain medium, and a frontreflective surface. The optical gain medium increases the gain ofelectromagnetic radiation that is not limited to any particular portionof the electromagnetic spectrum, but that may be visible, infrared,and/or ultraviolet light. An emitter may include or consist essentiallyof multiple beam emitters such as a diode bar configured to emitmultiple beams (i.e., each diode in the bar emits a single beam).

The term “substantially” or “approximately” means±10% (e.g., by weightor by volume), and in some embodiments, ±5%. The term “consistsessentially of” means excluding other materials that contribute tofunction, unless otherwise defined herein. Nonetheless, such othermaterials may be present, collectively or individually, in traceamounts. Reference throughout this specification to “one example,” “anexample,” “one embodiment,” or “an embodiment” means that a particularfeature, structure, or characteristic described in connection with theexample is included in at least one example of the present technology.Thus, the occurrences of the phrases “in one example,” “in an example,”“one embodiment,” or “an embodiment” in various places throughout thisspecification are not necessarily all referring to the same example.Furthermore, the particular features, structures, routines, steps, orcharacteristics may be combined in any suitable manner in one or moreexamples of the technology. The headings provided herein are forconvenience only and are not intended to limit or interpret the scope ormeaning of the claimed technology.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing will be more readily understood from the followingdetailed description of the invention, in particular, when taken inconjunction with the drawings, in which:

FIGS. 1A and 1B schematically illustrate a conventional beam-combiningsystem that may be used to pattern or cut material.

FIGS. 2A and 2B schematically illustrate shortened WBC systems withnon-confocal combining optics.

FIG. 2C illustrates a compact non-confocal dual lens WBC system.

FIG. 3 illustrates a position-to-angle WBC system devoid of an opticalcombining element.

FIG. 4 schematically illustrates a WBC laser system using a curvedgrating to increase brightness.

FIG. 5 schematically illustrates a feedback system for controlling laseroperation in accordance with an embodiment of the invention.

DETAILED DESCRIPTION

Aspects and embodiments relate generally to beam sources that achievehigh power and high brightness using wavelength beam combining (WBC).The approaches and embodiments described herein may apply to 1D and 2Dbeam-combining systems along the slow-axis, fast-axis, or otherbeam-combining dimension. In addition, the techniques may apply toexternal- and non-external-cavity WBC systems.

Representative WBC Systems

A conventional external-cavity 1D WBC system that may be utilized withembodiments of the present invention is shown in FIG. 1. The illustratedsystem utilizes a 1D bar 102 of diode lasers having a back-reflectivesurface 104, a gain medium 106 with two or more diode emitters, and afront reflective surface 108. The system also includes a combining optic110 (e.g., a lens), a dispersive element 112, and a partially reflectingoutput coupler 114. The combining optic or lens 110 is located a focaldistance 120 a away from the front reflective surface 108 of the diodebar 102, and the dispersive element 112 is located a focal distance 120b away from the optic 110; typically, the focal distances 120 a, 120 bare identical and correspond to the focal planes of the optic 110. Theoutput coupler 114 reflects a portion 122 of the generated beams to thedispersive element 112 and allows the remaining portion 125 to passthrough as the system output.

For explanatory purposes, FIG. 1A shows a single beam. In fact, thediode bar 102 generates a plurality of beams 130 as illustrated in FIG.1B. The combining lens overlaps the chief rays from all of the emittingelements on the dispersive element 112, and collimates each beam in bothaxes orthogonal to the direction of propatation.

A more compact WBC system may be achieved as shown in FIGS. 2A and 2B byintentionally placing the diode bar 102 or the dispersive optic 112 at aposition other than the focal plane of the combining optical element110. If the combining optical element 110 is disposed less than a focallength from the diode bar 102, one or more additional collimating optics210 may be located in front of or behind the dispersive element 112 andin front of the partially reflective output coupler 114. Thisarrangement can reduce the optical path length between the diode bar 102and output coupler by almost a full focal length of combining element110, particularly when the combining element 110 is placed adjacent tothe front surface/facet 108 of the diode bar 102.

In a variation of this embodiment, also shown in FIG. 2A, a collimatingoptic 212 may be disposed in front of each emission point along thefront surface/facet 108 of the diode bar 102 and in front of thecombining optical element 110, which still results in a shortened WBCsystem. In this variation, the collimating optic(s) 212 may comprise orconsist of an array of micro-optical fast-axis collimating (FAC) lenses,slow-axis collimating (SAC) lenses, or combination of both. Bycollimating each beam, proper wavelength stabilization feedback intoeach of the diode elements is ensured. This enables each emissionelement to produce a unique wavelength that is stabilized with lesssusceptibility to shifting, producing a multi-wavelength output beamprofile of high brightness and power is achieved.

As shown in FIG. 2A, the dispersive element or diffraction grating 112is placed substantially at the back focal plane of the lens 110. Asdrawn (the first approximation), the lens 110 with focal length F1 onlyconverges the chief rays for each of the diode elements. This can beunderstood from the Gaussian beam transformation by reference to thelens equation:

${\frac{1}{s + \frac{z_{R}^{2}}{s - f}} + \frac{1}{s^{''}}} = \frac{1}{f}$where s and s″ are the input and output waist locations, Z_(R) is theRaleigh range, and f is the focal length. Thus, the chief rays 160 areoverlapping at the grating 112 while each individual beam is stilldiverging (as indicated at 162 by dashed lines). The diverging beams 162may or may not be later collimated by an optical element, such as theoptic 210. With all the diode element beams overlapped on the dispersiveelement 112, the output beam quality is generally that of a singleemitter. Again, one advantage of this system is the size may beconsiderably smaller than, for example, a two-focal-length spacingbetween diode elements and the dispersive element 112. In some instancescases, the beam path is reduced by almost half or more. The spacing asdescribed herein may be slightly longer, equal to, or slightly shorterthan F1.

Alternatively, an embodiment devoid of collimating optic(s) 210 isillustrated in FIG. 2B. The combining optical element 110 is placed afocal length from the front facet 108 of the diode bar 102 and, as aresult, collimates the light from each diode element. A reduced systemsize is still achieved by placing the dispersive element 112 less than afocal length away from the combining optical element 110. The brightnessof the multi-wavelength beam is still increased as compared to theinitial array of beams produced by the diode bar 102, but there may besome degradation in the output beam quality. In one variation of thisembodiment, the diode elements 102 are a single 10-mm wide bar with 47emitters. Each emitter may have a FAC lens (not shown) and no SAC lens.Inclusion of a SAC lens does not change the results. The focal length ofthe FAC lens in this variation may be 910 μm, and the diode bar mayoperate at a 1 μm wavelength. With each beam being diffraction-limitedalong the fast axis, the typical full divergence after the FAC lens isabout 1 milliradian (mrd). Along the slow axis, the beam diverges about100 mrd. We assume that the combining optical element 110 or transformlens has a focal length of 150 mm. The output beam quality M² isapproximately:

$M^{2} = {\frac{\pi\;\theta}{4\lambda}\sqrt{( {{zx}\text{/}f} )^{2} + 1}}$where λ=1 μm, z is the distance after the lens to the grating and centerat the back focal plane, x=10 mm is the dimension of the array, and θ isthe individual beam divergence after the grating.

FIG. 2C illustrates a WBC arrangement that enables a shortened beampathway, and substantially separates the functions of combining chiefrays and collimating diverging rays into two separate optical elements(or systems) positioned before the dispersive element 112. The combiningelement 210 is positioned at a distance substantially less than itsrespective focal length F1 away from the front aperture 108 on one sideand approximately a focal length F1 away from the dispersive element 112on the other side. This allows combining element 110 to direct the chiefrays from each diode emitter of the diode bar 102 to overlap (orsubstantially overlap) on the dispersive element 112. At the same time,the collimating optical element 210 is placed approximately a focallength F2 away from the front aperture of each diode emitter on one sideand a distance less than focal length F2 from the dispersive element 112on the other side. The primary function of the collimating opticalelement 210 is to collimate the diverging rays. One skilled in the artwill readily appreciate that both elements 110, 210 have optical poweralong the same dimension and as a result will have some effect on thephysical placement of each optical element with respect to the frontaperture and dispersive element. This interdependency may managed inpart by placing the optical element 110 close to the emission apertureand the optical element 210 close to the dispersive element 112. Thisensures that the combining optical element 110 primarily dominates thecombining of the chief rays on the dispersive element 112, but isinfluenced by the prescription of the collimating optical element 210and vice versa.

Other designs may reduce system size and even the need for opticalcombining elements through alternative position-to-angle methods. Forexample, FIG. 3 illustrates a WBC system devoid of an optical combiningelement. Each diode element 102 (which may have as few as a single diodeemitter) may be mechanically positioned in a manner that the chief rays(solid lines 160) exiting the diode elements 102 overlap at a commonregion on the dispersive element 112 as shown. (In other variations ofthis embodiment, and similar to that shown in FIG. 2B, the beams do notcompletely overlap at the dispersive element, but the spatial distancebetween each along a combining dimension is reduced.) The divergingrays, illustrated by dashed lines 162, are collimated by collimatingoptic(s) 210 positioned between the dispersive element 112 and thepartially reflective output coupler 114. (Some variations of thisembodiment include replacing collimating optic 124 with individual FACand/or SAC lenses positioned at the front surface or facet of each diodebar.) This embodiment thus increases brightness while reducing thenumber of optical elements required as well as reducing overall systemsize.

In another embodiment, shown in FIG. 4, a curved diffraction grating 412is placed a focal length F1 away from the diode bar 402. The curveddiffraction grating 412 combines the emitted beams into amulti-wavelength beam that is transmitted to the partially reflectiveoutput coupler 114, which reflects a portion of the beams back towardsthe curved diffraction grating 412. The wavelengths of the reflectedbeams are then filtered by the diffraction grating 412 and transmittedback into each emitter of diode bar 102, whereby each emitter isstabilized to a particular wavelength. The maximum brightness producedby this type of system generally hinges on the amount of power thecurved diffraction grating 412 can handle. This optical architecturereduces the number of optical elements and shortens the beam path whileincreasing the brightness of a multi-wavelength output beam. Degradationof the beam quality results as a function of the beam width 475 over theentire distance of the beam profile 485.

Combination with Interferometry

Any of the foregoing optical architectures can be used in high-powermaterials-processing applications such as cutting, drilling, andpatterning. In accordance with embodiments of the present invention, theoutput of the WBC source is passed through one or more elements creatingan interferometric output that is analyzed to determine, in real time,the depth or height of the surface that the beam strikes. Arepresentative architecture is shown in FIG. 5. The multi-wavelengthbeam output of any of the WBC systems shown in FIGS. 1-4 (and indicatedat 505) is used to process a machining surface 510. The WBC system 505provides an input for machining a surface 510 to create desired featuresor cuts. The beam passes through a beamsplitter cube 515 disposedbetween the multi-wavelength source and the machining surface 510. Aportion 518 of the beam is diverted to a movable mirror 520 (e.g., asurface having a reflectivity ≧99%), which is configured for translationalong the optical axis of the beam 518; thus, the mirror 520 can shiftposition to the location indicated in phantom. A portion 522 of thereflected beam is transmitted back through the beamsplitter 515 onto aninterferometric detector system 525, where this beam portion 522 is usedas a first reference for comparison. The portion 530 of the beam thatpasses directly through the beamsplitter 515 is transmitted onto themachining surface 510, where a portion 532 of the beam is reflected backto the beamsplitter 515 and then diverted onto the interferometricdetector as a second reference to be compared with the first reference.In order to accurately determine the change of depth position of thecuts and/or welds on the machined surface, the lateral position of thereflective mirror 520 may be adjusted to match up with the coherencewavelength of one or more wavelengths. This occurs when the a wavelengthundergoes constructive or destructive interference at the detector 525.

The wavelength or wavelengths that undergo interference depends on thedifference between (i) the distance between the center point 540 of thebeamsplitter 515 and the mirror 520 and (ii) the distance between thecenter point 540 and the surface 510. Accordingly, adjusting theposition of the mirror 520 until one of the output wavelengths undergoesinterference allows calculation of the distance to the surface 510 and,hence, the depth of a groove or the height of a feature relative to abaseline—i.e., a neutral level whose distance from the center point 515was previously established. By utilizing a 2D array of beam sources andcausing relative movement between the surface 510 and the beam 530, a 3Drepresentation of the surface 510 can be built up.

The detector 525 may report the instantaneous depth/height informationto a controller 550, which controls the operation of the WBC source 505(i.e., it actives the source 505 and controls beam parameters asappropriate during processing). The controller 550 also operates aconventional positioning system to cause relative movement between thebeam output of the WBC source 505 and the surface 510. The positioningsystem may be any controllable optical, mechanical or opto-mechanicalsystem for directing the beam through a processing path along a 2D or 3Dworkpiece. During processing, the controller may operate the positioningsystem and the WBC source 505 so that the output beam traverses aprocessing path along the surface 510. The processing path may beprovided by a user and stored in an onboard or remote memory, which mayalso store parameters relating to the type of processing (cutting,welding, etc.) and the beam parameters necessary to carry out thatprocessing. In this regard, a local or remote database may maintain alibrary of materials that the system will process, and upon userselection of a material, the controller 550 queries the database toobtain, for example, a relationship between output power and cuttingdepth.

As is well understood in the plotting and scanning art, the requisiterelative motion between the beam and the workpiece may be produced byoptical deflection of the beam using a movable mirror, physical movementof the laser using a gantry, lead-screw or other arrangement, and/or amechanical arrangement for moving the workpiece rather than (or inaddition to) the beam. As the controller 550 receives real-time feedbackregarding the depth or height of a feature, it alters the output poweror other parameter of the WBC output beam (e.g., M², beam parameterproduct, etc.) so that the programmed height or depth is maintainednotwithstanding variation in material properties. That is, the point onthe surface 510 at which the distance to the center point 540 iscomputed may be just behind the beam (so that, e.g., the depth of thecut just made is measured). The controller 550 may also store, forexample, power levels and corresponding cutting depths for calibrationor to correct stored values.

The controller 550 also controls an actuator 555 for translating themirror 520 along the axis of the beam 518. For example, the controller550 may vary the lateral position of the mirror 520 until interferenceis detected by the detector 525, or until a particular wavelengthundergoes interference.

The controller 550 may be provided as either software, hardware, or somecombination thereof. For example, the system may be implemented on oneor more conventional server-class computers, such as a PC having a CPUboard containing one or more processors such as the Pentium or Celeronfamily of processors manufactured by Intel Corporation of Santa Clara,Calif., the 680x0 and POWER PC family of processors manufactured byMotorola Corporation of Schaumburg, Ill., and/or the ATHLON line ofprocessors manufactured by Advanced Micro Devices, Inc., of Sunnyvale,Calif. The processor may also include a main memory unit for storingprograms and/or data relating to the methods described above. The memorymay include random access memory (RAM), read only memory (ROM), and/orFLASH memory residing on commonly available hardware such as one or moreapplication specific integrated circuits (ASIC), field programmable gatearrays (FPGA), electrically erasable programmable read-only memories(EEPROM), programmable read-only memories (PROM), programmable logicdevices (PLD), or read-only memory devices (ROM). In some embodiments,the programs may be provided using external RAM and/or ROM such asoptical disks, magnetic disks, as well as other commonly used storagedevices. For embodiments in which the functions are provided as one ormore software programs, the programs may be written in any of a numberof high level languages such as FORTRAN, PASCAL, JAVA, C, C++, C#,BASIC, various scripting languages, and/or HTML. Additionally, thesoftware may be implemented in an assembly language directed to themicroprocessor resident on a target computer; for example, the softwaremay be implemented in Intel 80x86 assembly language if it is configuredto run on an IBM PC or PC clone. The software may be embodied on anarticle of manufacture including, but not limited to, a floppy disk, ajump drive, a hard disk, an optical disk, a magnetic tape, a PROM, anEPROM, EEPROM, field-programmable gate array, or CD-ROM.

The above description is merely illustrative. Having thus describedseveral aspects of at least one embodiment of this invention includingthe preferred embodiments, it is to be appreciated that variousalterations, modifications, and improvements will readily occur to thoseskilled in the art. Such alterations, modifications, and improvementsare intended to be part of this disclosure, and are intended to bewithin the spirit and scope of the invention. Accordingly, the foregoingdescription and drawings are by way of example only.

What is claimed is:
 1. A system for processing a workpiece, the systemcomprising: a wavelength beam combining (WBC) emitter for emitting amulti-wavelength output beam comprising optical radiation having aplurality of wavelengths; a movable surface reflective to all of thewavelengths in the multi-wavelength output beam; a photodetector; abeamsplitter for (i) diverting a portion of the multi-wavelength outputbeam to the movable reflective surface and (ii) diverting a portion of areflection of the multi-wavelength output beam from a surface of theworkpiece to the photodetector, the photodetector being aligned with themovable reflective surface to receive therefrom a reflection of thediverted portion of the multi-wavelength output beam; a database storingparameters relating process types and material compositions tooutput-beam properties; and a controller, coupled to the WBC emitterdevice and the photodetector, for (i) computing a height or depth of afeature on the surface of the workpiece based at least in part on asignal from photodetector and (ii) controlling a property of themulti-wavelength output beam, in accordance with one or more parametersin the database, to process the surface of the workpiece to thereby forma feature in or on the surface of the workpiece.
 2. The system of claim1, wherein the height or depth is determined based on a distance betweenthe beamsplitter and the surface of the workpiece.
 3. The system ofclaim 1, wherein the signal from the photodetector indicates a degree ofinterference between the reflection of the multi-wavelength output beamfrom the surface of the workpiece and the reflection from the movablereflective surface of the diverted portion of the multi-wavelengthoutput beam.
 4. The system of claim 1, wherein the controller isconfigured to control a parameter of the multi-wavelength output beam tomaintain a target distance between the beamsplitter and the surface ofthe workpiece.
 5. The system of claim 4, wherein the controlledparameter of the multi-wavelength output beam is power.
 6. The system ofclaim 4, wherein the controlled parameter of the multi-wavelength outputbeam is beam parameter product.
 7. The system of claim 1, wherein theWBC emitter comprises: a plurality of beam emitters each emitting abeam; a combining optical element arranged to receive the plurality ofbeams and cause a chief ray of each of the beams to converge along abeam-combining axis; a dispersive element, positioned along thebeam-combining axis, to receive and transmit the converging chief rays;and a partially reflective output coupler arranged to receive thetransmitted beams from the dispersive element, to reflect a portion ofthe transmitted beams toward the dispersive element, and to transmit themulti-wavelength output beam.
 8. The system of claim 1, wherein thecontroller is configured to control a parameter the property of themulti-wavelength output beam to cut, etch, anneal, drill, solder, and/orweld the workpiece.
 9. The system of claim 1, wherein the controlledproperty of the multi-wavelength output beam comprises at least one ofpower or beam parameter product.
 10. The system of claim 1, wherein thefeature has a height above the surface of the workpiece or has a depthbelow the surface of the workpiece.
 11. A method for processing aworkpiece, the method comprising the steps of: causing emission of anoutput beam from a wavelength beam combining (WBC) emitter, the outputbeam comprising optical radiation having a plurality of wavelengths;diverting a portion of the multi-wavelength output beam to a movablesurface reflective to all of the wavelengths in the multi-wavelengthoutput beam; diverting a portion of a reflection of the multi-wavelengthoutput beam from a surface of the workpiece to a photodetector;receiving, at the photodetector, a reflection from the movablereflective surface of the diverted portion of the multi-wavelengthoutput beam, the reflection including all of the wavelengths in themulti-wavelength output beam; computing a height or depth of a featureon the workpiece based at least in part on a signal from thephotodetector; and processing the surface of the workpiece with themulti-wavelength output beam to thereby form a feature in or on thesurface of the workpiece, wherein the surface of the workpiece isprocessed based on stored parameters relating process types toproperties of the multi-wavelength output beam.
 12. The method of claim11, wherein the height or depth is determined based on a distancebetween the surface of the workpiece and a location where the portion ofthe reflection is diverted.
 13. The method of claim 11, wherein thesignal from the photodetector indicates a degree of interference betweenthe reflection of the multi-wavelength output beam from the surface ofthe workpiece and the reflection, from the movable surface, of thediverted portion of the multi-wavelength output beam.
 14. The method ofclaim 11, further comprising the step of controlling a parameter of themulti-wavelength output beam to maintain a target distance between thebeamsplitter and the surface of the workpiece.
 15. The method of claim14, wherein the controlled parameter of the multi-wavelength output beamis power.
 16. The method of claim 14, wherein the controlled parameterof the multi-wavelength output beam is beam parameter product.
 17. Themethod of claim 11, wherein processing the surface of the workpiececomprises at least one of cutting the workpiece, etching the workpiece,annealing the workpiece, drilling the workpiece, soldering theworkpiece, or welding the workpiece.
 18. The method of claim 11, whereinthe surface of the workpiece is processed in response to user selectionof a material composition of the workpiece.
 19. The method of claim 11,wherein processing the surface of the workpiece comprises controlling aproperty of the multi-wavelength output beam in accordance with thestored parameters.
 20. The method of claim 19, wherein the controlledproperty of the multi-wavelength beam comprises at least one of power orbeam parameter product.
 21. The method of claim 11, wherein the featurehas a height above the surface of the workpiece or has a depth below thesurface of the workpiece.